I saw really big power savings when I started using TuneD. Such a huge upgrade for Linux users! From 8 months ago, going from 120 -> 85W. More recently got my desktop down to 65, yay. https://news.ycombinator.com/item?id=42636350

There's also API compatibility with the power-profiles-daemon, which didn't ever help me that much (I'd also done some basic tuning myself), and which has been unmaintained for a while now. But there's still a variety of utilities which target the old ppd.